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VGA51 Specification

3. Specification

The adapter currently supports the following:

A. Modes of operation:
* Text modes:
80x25 16 colors (standard text mode)
80x30 16 colors (extended lines mode)
* Planned v.2 provides in addition 8x8 font based text modes of: 80x50 & 80x60 in 16 colors. 
* Graphic modes:
320x200 16 colors
640x400 mono (b&w) 

B. I/O Ports map: 
* port base address: 
16-bit configurable by on board dip switches
* port offsets: 
00-05h - configure vga51 & auxiliary functions
(mode, cursorX, cursorY, cursorShape, ram page, console config), 
additional dip switch: 4 position to force mode at adapter boot 

C. Memory organization: 
Video RAM (vram): parallel, video memory mapped: 32kB (A0-A14), 8-bit data (D0-D7)
Adjustable video memory access window: 8kB, 16kB and 32kB to fit most of the 8-bit systems with 64kB address range. 
* Physical memory:
- on board video RAM of 32000 bytes
- on board character generator ROM 4kB (stores 256 ASCII chars defined as 8x16 raster.
- Planned v.2 provides in addition 8x8 font map to support 80x50 & 80x60 text modes. 
In text modes character video ram is organized just like in PC running text mode, ascii char byte (0 offset) + attribute byte (+1 offset).
Addresses: for 25 lines mode: 4000 bytes (2000 for ASCII char index + 2000 attributes), address: 0000-0F9Fh
For 30 lines mode: 4800 bytes (2400 and 2400 respectively as above), address: 0000-12BFh
For high density lines modes of 50 & 60 lines when 8x8 font is being used, the above address range doubles respectively. 
For graphics mode, linear video ram size is: 32000 bytes, address: 0000-7CFFh.

D. Extensions
* VGA51 adapter design supports optional use of internal EEPROM/Flash type storage for BIOS extension (CPU specific), which contain user functions to easily manipulate characters write, char attribute assignment, cursor position, console typing mode, etc. (similar to PC int10h functions). 

E. Interrupts 
1. Video interrupt for video frame blanking. Connected to desired IRQ line by setting jumper.
2. Console ASCII character received & ready in port buffer. Connected to desired IRQ line by setting jumper.

F. Interfaces
1. ISA (8-bit), S100 bus & MCS51 (custom)
2. PS/2 port for keyboard (in console version "C")
3. One or Two (in DUAL) DB15HD VGA outputs for VGA compatible monitor(s). 

* Output(s) details
One standard DB-15 analog (VGA compatible)
runs with all monitors, using physical scan modes of:
640x480 60Hz
640x400 70Hz
which are supported by all older and new monitors equipped with DB-15 analog connector including HD monitors and TV sets. 
Two standard DB-15 analog outputs in DUAL monitor version of the VGA51 to operate 2 monitors simultaneously in the following mode combinations:
a) Monitor 1 in text & monitor 2 in graphics 
b) M.1 text & M.2 text (same # of lines as in M.1) , M.2 uses separate memory space hence it can display different content 
c) text only mirrored on M.1 & M.2
d) graphics only mirrored on M.1 & M.2
* standard text modes with 25 and 30 lines with 80 characters per line use 8x16 font
* high line text modes (8x8 font) with 50 and 60 lines are only supported in b) and c).
The above spec has been successfully  tested on the following monitors/TV sets:
- CRT Viewsonic E70f monitor (2001)
- LCD Samsung Syncmaster 930B monitor (2005)
- LCD Samsung SyncMaster P2770HD monitor (2012)
- LCD HDTV Samsung LN40A650 (2008)
- LCD HDTV Samsung LN55C650 (2010)
- LCD HDTV Samsung 46" (type to be added here once removed from the wall vesa mount)

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